1. Field of the Invention
The present invention relates to a compressor, for compressing a refrigerant gas, which can be applied to, for example, an air-conditioner incorporated in a vehicle. More particularly, the present invention relates to compressor having a piston rotation restricting structure for restricting rotation of a piston around the axis of the piston itself.
2. Description of the Related Art
A compressor of the above type will be explained as follows. A crank chamber is formed in a housing, and a drive shaft extends through the crank chamber and is rotatably supported by the housing. A swash plate is connected to the drive shaft in the crank chamber so that the swash plate can be rotated with the drive shaft. Cylinder bores are formed in the cylinder block composing a portion of the housing. The piston has a head portion and a neck portion which are axially connected with each other. The head portion of the piston is inserted in the cylinder bore, and the neck portion of the piston is located in the crank chamber outside the cylinder bore. Shoes are housed in this neck portion. The piston is connected to the swash plate via the shoes. Rotation of the swash plate caused by rotation of the drive shaft is converted into a reciprocating motion of the piston via the shoes. Therefore, refrigerant gas is compressed in the cylinder bore.
In the compressor constructed as described above, since the piston is connected to the swash plate via the shoes, and the piston tends to rotate around the axis of the piston itself, vibration and noise are possibly caused by the interference of the neck portion of the piston with the swash plate which rotates at high speed. Therefore, a piston rotation restricting structure is provided in the above compressor. That is, a piston side rotation restricting member is arranged in the neck portion of the piston. A housing side rotation restricting member is provided in the housing at the crank chamber to engage with the piston side rotation restricting member while allowing reciprocating motion of the piston. Rotation of the piston around the axis of the piston itself is restricted by the engagement of the piston side rotation restricting member with the housing side rotation restricting member.
However, when the above rotation restricting structure is provided, a new problem is caused in which the number of sliding portions between the piston and the housing is increased, that is, a sliding portion, between both the rotation restricting sections, is newly added to the number of the sliding portions. Therefore, power loss caused in the compressor is increased. In order to solve the above problem, there is proposed, as a countermeasure, to form an abrasion-resistant coating, for example, on the piston side rotation restricting member. However, even if an abrasion-resistant coating is provided, it has a problem of durability that it will be worn out by the repetition of sliding motion between the piston side rotation restricting member and the housing side rotation restricting member.
In this case, the crank chamber is supplied with refrigerant gas which enters the crank chamber, for example, as blow-by gas. This refrigerant gas contains mist of lubricant. If the supplied lubricant into the crank chamber can be supplied to a gap between the piston side rotation restricting member and the housing side rotation restricting member, fluid lubrication can be effectively accomplished between both sliding rotation restricting members. However, the lubricant supplied into the crank chamber is pushed back by the end surface of the neck portion of the reciprocating piston. Therefore, only a small quantity of lubricant enters a gap between both rotation restricting members.
The present invention is accomplished to solve the above problems of the prior art. It is an object of the present invention to provide a compressor having a piston rotation restricting structure capable of supplying a sufficiently large quantity of lubricant from the crank chamber to a gap between the piston side rotation restricting member and the housing side rotation restricting member.
In order to accomplish the above object, according to the present invention, there is provided a compressor comprising: a housing having cylinder bores and a crank chamber; pistons having head portions and neck portions arranged such that the head portions are reciprocatingly inserted in the cylinder bores and the neck portions connected to the head portions; a drive shaft extending through the crank chamber and rotatably supported by the housing; a cam plate such as a swash plate arranged in the crank chamber and rotatable with the drive shaft; shoes arranged between the cam plate and the neck portions of the pistons; a piston rotation restricting structure comprising a first rotation restricting member formed on the neck portion of each piston, and a second rotation restricting member provided in the housing so that the first rotation restricting member can contact the second rotation restricting member to restrict rotation of the piston about its own axis while allowing reciprocating motion of the piston; the first rotation restricting member comprising axially spaced end surfaces, and an outer peripheral surface between the end surfaces; and an inclined guide surface formed in one end surface of the first rotation restricting member and inclined toward the outer peripheral surface for guiding lubricant from the crank chamber into a gap between the first rotation restricting member and the second rotation restricting member when the piston moves in one direction or in the other direction.
In this compressor, lubricant is introduced from the crank chamber into the inclined guide surface by the reciprocating motion of the piston and supplied to a gap between the first rotation restricting member and the second rotation restricting member. Accordingly, it is possible to supply a sufficiently large quantity of lubricant to a gap between the first rotation restricting member and the second rotation restricting member. Accordingly, fluid lubrication can be effectively accomplished between both sliding rotation restricting members.
Preferably, the inclined guide surface comprises a single flat surface. When this structure is adopted, the inclined guide surface can be easily machined.
Preferably, the inclined guide surface comprises a flat surface and guide walls provided on both sides of the flat surface so that the entire inclined guide surface is formed into a recessed shape. Preferably, the entire inclined guide surface is formed into a recessed shape in which a plurality of flat surfaces, which are arranged in parallel to the axis of the piston and are connected with each other at a merging bottom line. Preferably, the inclined guide surface is composed of a concavity on which the central portion is deeper than both the side portions.
According to the above structure, most of the lubricant introduced into the inclined guide surface by the reciprocating motion of the piston is prevented, by the inclined guide surface which is formed into a recessed shape, from leaking out onto the sides. Therefore, the lubricant can be positively supplied to both the rotation restricting members.
Preferably, an abrasion-resistant coating is provided on at least one of an engaging surface of the first and second rotation restricting members.
According to the above structure, even when an absolute quantity of lubricant in the crank chamber is small so that a sufficiently effective fluid lubrication cannot be accomplished between both the rotation restricting members, the first and second rotation restricting members can slide on each other with a low friction coefficient by solid lubrication conducted by the abrasion-resistant coating. On the contrary, when an absolute quantity of lubricant in the crank chamber is large, a sufficiently large quantity of lubricant can be supplied to a gap between both the rotation restricting members by the inclined guide surface. Therefore, the main lubrication between both the rotation restricting members changes from solid lubrication conducted by the abrasion-resistant coating to fluid lubrication conducted by lubricant, and at the same time, the abrasion-resistant coating is protected by the fluid lubrication. Therefore, the durability can be enhanced.
Preferably, the inclined guide surface is formed on one end face of the first rotation restricting member located on the side opposite to the head portion.
In the above structure, the inclined guide surface of the piston can be easily performed, for example, finish grinding can be easily conducted on the inclined guide surface, because one end face opposed to the head portion of the first rotation restricting member is a terminal end face of the piston part and the inclined guide surface can be easily machined here. However, one end face on the side of the head portion of the first rotation restricting member is located in the middle of the piston part in the axial direction. Therefore, it is difficult to conduct machining of the inclined guide surface on this face.
Preferably, one arrangement of the second rotation restricting member which is desirable at present is realized. Thus, the second rotation restricting member comprises an inner peripheral surface of the housing surrounding the crank chamber around the drive axis.